1. Field of the Invention
The present invention relates to the field of liquid chromatography. More particularly, the present invention is directed to an improved method for sealing liquid chromatographic columns and improved closure members for use therewith.
2. Description of the Prior Art
Chromatography is a method for separating individual compounds in a mixture by distributing the compounds between heterogenous phases. A column packing material (or media), forming a stationary phase, generally has a large surface area through which a liquid mobile phase is allowed to flow. Chemical compounds in the mobile phase are maintained in the system for a time that is dependent upon the affinity of the particular compounds for the stationary phase. Multiple component mixtures can, with chromatography, be separated into single components in a single step procedure.
Chromatographic separations can be carried out efficiently in columns slurry packed with microparticulate media. The slurry is uniformly and rapidly compacted into. a column under pressure. The slurry is maintained at very high pressure and density to achieve the most efficient end results.
A chromatographic column includes a cylindric column body, a fixed end plate covering one end of the column body, a piston slidable within the column body, an intake opening through the piston, a discharge opening through the end plate, a first porous frit secured to the piston and covering the intake opening, and a second porous frit secured to the end plate and covering the discharge opening. A slurry containing the packing material, such as a granular silica or polymeric media, is placed within the column body and the piston is moved toward the fixed end plate to compress the slurry. The pores of the frits are sized to permit the liquid of the slurry to flow out the discharge opening while preventing discharge of the packing material. An example of a prior art chromatographic column 202 and a compression device 220 which together comprise a chromatographic apparatus 200 is shown in FIG. 1. Column 200 is placed on the compression device 220 on a plate 212 at the end of a hydraulic compression cylinder 214. Column 200 has a flange 206 with a number of mounting holes 207 that fit over a group of threaded rods or bolts 210 extending upward from plate 212. Once mounted, nuts 208 secure the flange onto plate 212. A piston 222 is secured to the end of a telescoping rod (not shown) that can be controlled by one or more controls 218 on pressing apparatus 220. The piston 222 and telescoping rod are typically powered by a pneumatic pump though line 216, which moves the telescopic rod. The piston 222 includes an intake opening and a feeding tube (neither of which are visible in FIG. 1), the latter of which can be mounted in a recess on either plate 212 or flange 206 or both to prevent the tube from being crushed when the column 202 is secured to plate 212. A chromatographic slurry is then loaded into the upper end of column 202, and end plate 204 is secured in place. End plate 204 includes a discharge opening for attaching an outlet tube. (of course, the terminology "intake" and "outlet" are arbitrary, because the direction of flow may be reversed, i.e., changed from the piston to the end cap or from the end cap towards the piston.)
Conventionally, when the chromatographic media within chromatographic column 202 is packed, a telescoping rod pushes piston 222 into the column. This compression packs the packing material to a predetermined pressure (which may typically be around 1,000 to 5,000 p.s.i., but these value are merely exemplary rather than limiting). It would be advantageous if the column were constructed so that the rod were not connected to the piston or the column (other than by pressing against the piston) so that the piston could remain in a compressed position within the column body, at least for a period of time, after the rod is retracted. Previous chromatographic columns have not been designed to allow a packed column to be removed from the pressing apparatus and set aside for future use in this manner, but it would be advantageous if it were possible to do so in this manner. In addition, pressing apparatuses have, until now, been constructed so that the apparatus can only be operated with the telescoping rod extending from its cylinder in only one orientation. It would be advantageous if, instead, the apparatus could be operated to extend the rod in either an upward or a downward orientation. Moreover, it would be advantageous if the column could be pivoted on the pressing apparatus to facilitate mixing of the chromatographic medium inside the column.